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Movie tech: How 'Gravity' threw Sandra Bullock into zero gravity

Sandra Bullock and George Clooney seem to float effortlessly in "Gravity," a terror-filled tale of two shuttle astronauts set adrift by a space disaster. But getting that zero-gravity effect to work took years of effort and million-dollar innovations.The first thing to get out of the way is that there are SPOILERS AHEAD. The second thing is to acknowledge that this is a fictional movie, not a phys
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Sandra Bullock and George Clooney seem to float effortlessly in "Gravity," a terror-filled tale of two shuttle astronauts set adrift by a space disaster. But getting that zero-gravity effect to work took years of effort and million-dollar innovations.

The first thing to get out of the way is that there are SPOILERS AHEAD. The second thing is to acknowledge that this is a fictional movie, not a physics lesson.

"There are places where they went against the science input that they got, because it blows up their story," Kevin Grazier, a planetary scientist who served as an adviser for "Gravity," told NBC News. "You have a choice. You can either say 'You can get to the ISS from here,' or you have a movie like 'Open Water' in space. That's a different movie, and that's not what they were shooting for."

So we won't dwell on how hard it would be to get from the Hubble Space Telescope to the International Space Station. That orbit-crossing trek is one of the movie's key plot points, but in reality it's virtually impossible — which led to huge logistical complications for NASA's final Hubble servicing mission.

We won't discuss how unlikely it would be for the planned shootdown of a satellite to cause an immediate catastrophe for a space shuttle. (Though it's important to note that the cascading effect of orbital debris, also known as the Kessler Syndrome, is a real concern — as the Russians found out this year.)

And we won't worry about the fact that the space shuttles aren't flying anymore. ("It's a typical historical drama," Grazier said.) If it's nitpicking you're after, check out the critiques from Time, The New York Times and Blastr.

Instead, we'll focus on how director Alfonso Cuaron and his team made Bullock and Clooney look good in zero gravity — so good that "Avatar" director James Cameron says "Gravity" is "the best space film ever done."

The work that went into pulling off that feat started years ago. Early on, the filmmakers decided to map out the entire movie with computer-generated imagery in a process they called previsualization, or "previs."

Animators adhered to the rules of objects in weightlessness as they previsualized the film, shot by shot, using highly detailed computer graphics. "We had to relearn physics, since we were all used to motion arcs that are determined by weight," senior animation supervisor David Shirk said in the movie's production notes. "We had to forget all that."

The animation shaped the actors' performances. "The live action was limited by what was preprogrammed in the previs. ... Due to the technological process, the margin for improvisation and spontaneity was very small, which added to the challenge for Sandra and George," Cuaron said.

Underwater and on a wire
But how do you get Sandra and George into zero-gravity mode? The weightless scenes in "Apollo 13" were filmed in short takes during parabolic airplane flights, which provide about a half-minute of weightlessness at a time. Those potentially nausea-inducing flights weren't an option for "Gravity" — in part because Cuaron was going for longer takes, and in part because Bullock has a deathly fear of flying.

"When we told her that that wasn't going to be [using] the system, and we have these other sets of tools, she didn't care how painful the other tools were," Cuaron told

For some scenes, the actors were filmed as they swam through their moves underwater. For others, they were hooked up with a 12-wire suspension system, and then filmed with robotic cameras while puppeteers pulled their strings. (The harness for the wires had to be made just right to fit under Sandra Bullock's skivvies.) Still other scenes were shot while the actors perched on a variety of rigs set up on a turntable. 

In the Light Box
The filmmakers' most innovative tool was the Light Box: a 20-foot-high (6-meter-high), boxy enclosure outfitted on the inside with 4,096 LED bulbs. Those lights could be programmed to project moving images of Earth and space. When the actors were locked up inside, computer-controlled robotic cameras captured close-ups under just the right lighting conditions — even for the scenes where Bullock looks as if she's spinning out of control. In reality, it's the light patterns that are spinning around her.

The Light Box was the brainchild of "Gravity" cinematographer Emmanuel Lubezki and visual-effects supervisor Tim Webber. "When the Light Box came together, I knew it was not only going to be the way I could light 'Gravity,' but would impact the way I light movies for years to come," Lubezki said.

Webber said the contraption also showed the actors what their characters were seeing during the scene being shot. "It was primarily so we could reflect the appropriate light on them, but it had the double benefit of being a visual reference for them, too," he said.

Putting it all together
The computer-generated animations and the live-action clips were blended together in post-production. All traces of wires, rigs and harnesses were digitally removed, and more special effects were added in. The result is so seamless that you see Bullock's panic-stricken face loom through a computer-generated helmet visor as she slingshots from the computer-generated depths of space to an extreme closeup. 

In the production notes, Webber said one of the biggest challenges was rendering the mist from the characters' breath on those helmet visors. "In reality, you wouldn't see as much breath on the visor because the systems in the suits keep the air very dry, but for us it was a visual indication of their tension," he said.

Grazier, who has been a consultant on Hollywood projects ranging from "Battlestar Galactica" to "Defiance," said science-fiction filmmakers seem to be paying increasing attention to the details. Even if they don't always obey the laws of physics, they still want the Right Stuff on the screen. That's why Cuaron and his team sought advice from Grazier as well as NASA astronauts Andy Thomas, Shannon Walker and Cady Coleman.

"They did their homework," Grazier said of the filmmakers. "They wanted to know which direction the switches went, which way the hatches opened."

Grazier said the stakes are likely to rise even higher as moviegoers become savvier about their sci-fi.

"Hollywood and science are starting to butt together more, partly because we're starting to lose our suspension of disbelief," Grazier told NBC News. "If an idea gets out that a movie is silly because this doesn't work, or that doesn't look right, that can affect your bottom line."

More about 'Gravity':

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding +Alan Boyle to your Google+ circles. To keep up with's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.